1. Field of the Invention
The present invention relates to a method of manufacturing a printed circuit board, and, more particularly to a method of manufacturing a printed circuit board in which a circuit portion such as a jumper circuit is formed by applying electroconductive ink such as copper paste in a connection portion of a printed circuit formed on an insulating substrate.
2. Related Art Statement
Hitherto, conventional printed circuit boards have been manufactured by forming predetermined printed circuits by performing etching of copper foil of so-called copper laminated boards formed by laminating copper foil on insulating substrates in accordance with predetermined layouts of the circuits.
In order to form a circuit such as a jumper circuit disposed between the printed circuits on such printed circuit boards, a manufacturing method, as shown in FIG. 5, has been developed such that a jumper circuit portion 4 structured by electrically connecting a connection terminal portion 4a is formed on a connection terminal portion 1 of a printed circuit 10 by applying and hardening electroconductive ink made of copper paste or other electroconductive paste by silk screen printing or the like. Recently, various types of electroconductive ink which can be advantageously used for forming circuits of the type described above have been developed.
However, when such circuits are formed by applying or performing silk screen printing of electroconductive paste such as copper paste, there arises a problem in terms of contact between the circuit terminal portion 1 in the copper foil on the printed circuit board and the electroconductive paste, that is the electroconductive ink. That is, since such electroconductive paste contains a great quantity of an electroconductive material such as carbon, silver or copper particles mixed in resin ink thereof for the purpose of improving electroconduction, the resin which can assist contact with the surface of the copper foil terminal is considerably reduced. As a result, electroconductive paste lacks sufficient adhesive force for realizing a contact with a metallic surface compared with normal resin ink, causing the electrical connection to become unreliable. In addition, its poor mechanical strength can cause it to peel due to the thermal shock generated when components are soldered.
To this end, an object of the present invention is to provide a method of manufacturing printed circuit boards capable of improving the electrical and mechanical strength required between electroconductive paste and the circuit terminal portion.